1. Introduction
This invention relates to the ortho-alkylation of phenols and more particularly, to the vapor phase ortho-alkylation of phenols by reaction of a non-ortho-alkylated phenol with an alcohol in the presence of a magnesium oxide alkylation catalyst.
2. Description of the Prior Art
In commonly-assigned Hamilton U.S. Pat. No. 3,446,856 there is disclosed and claimed a method for methylating the ortho positions of phenol by the vapor phase reaction of a phenol with methanol in presence of magnesium oxide at a catalyst bed temperature in the range of 475.degree. to 600.degree. C. Under the conditions described in the Hamilton application, phenol is selectively ortho-methylated in yields of 95%. Thus, the reaction provides means for economically converting phenol to ortho-cresol, a useful disinfectant and wood preservative and for converting both phenol and ortho-cresol to 2,6-xylenol, a monomer which can be polymerized to form poly-2,6-xylenol, a high performance thermoplastic material.
While the Hamilton invention provides an economic synthesis for both 2,6-xylenol and ortho-cresol from phenol, the service life of the magnesium oxide catalyst is relatively short due to the high temperature at which the reaction is required to take place-i.e., about 40 to 60 hours service life at the typical temperature of about 530.degree. C. After this period of time, catalyst must be regenerated before it can be re-used. Regeneration is a costly procedure as it involves shutting down the reactor, passing inert gases containing oxygen through the reactor, and gradually increasing the oxygen content in the inert gases until approximately 16 to 20% oxygen is contained in the gas stream.
In addition to the above difficulties, the magnesium oxide catalyst of the Hamilton patent is only moderately strong and frequent regenerations cause pellets of the catalyst to fragment. In addition, the use of modified magnesium oxide in powder form or in the form of a weakly sintered composite results in a relatively large induction period of maximum selectivity. The term "induction period" may be defined as the period commencing with the start-up of the reaction to the time at which the catalyst reaches and maintains maximum ortho-alkylation selectively. Obviously, with a long induction period and a short catalyst life, the overall process becomes more costly.
Many of the above-noted difficulties are overcome by the processes of abandoned Van Sorge U.S. Pat. application Ser. Nos. 717,919 filed Apr. 1, 1968, 846,925 and abandoned application 846,973, now abandoned application 846,967; and, incorporated herein by reference. In these applications, processes are disclosed for the ortho-alkylation of phenol comprising the reaction of a non-ortho-substituted phenol with an alcohol in the presence of a modified magnesium catalyst comprising magnesium oxide having an inert binder such as a polymeric biner, silica and manganese oxide. In all of the above applications, one of the improvements is increased service life of the catalyst. However, even with the improvement in service life afforded by the inventions of the above applications, it is desirable to further increase the service life of the catalyst to decrease the overall cost of the process.